發(fā)布時間：2019-06-02 12:45

【摘要】：自從20世紀(jì)60年代激光器問世以來,激光器已經(jīng)被廣泛應(yīng)用于通訊、生物、醫(yī)學(xué)、國防、軍事等領(lǐng)域,對人們的生活產(chǎn)生了革命性的變化。目前常用的激光器主要有固體激光器、氣體激光器、染料激光器和半導(dǎo)體激光器等,它們都具有穩(wěn)定性好的特點(diǎn),但是它們的致命缺點(diǎn)是體積大,這使得它們越來越不能滿足集成光學(xué)發(fā)展的需要。集成光學(xué)的發(fā)展越來越需要微型激光器,因此近年來微型激光得到了廣泛的研究。目前被廣泛研究的微型激光器主要有法布里-珀羅(F-P)腔激光器、分布式反饋激光器(FDB)、微腔激光器及碟片激光器等幾種類型,這幾類激光器都具有閾值低、體積小、光譜較窄、調(diào)制速率高等特點(diǎn),但它們的制作工藝都非常復(fù)雜,有的需要高精度的鍍膜技術(shù),成本很高。膽固醇液晶(cholesteric liquid crystal,CLC)因其周期性螺旋結(jié)構(gòu)和高雙折射率的特點(diǎn),會形成布拉格反射帶,相當(dāng)于一維光子晶體。與傳統(tǒng)的光子晶體相比,膽固醇液晶具有很多獨(dú)特的特點(diǎn)。首先膽固醇液晶反射帶的中心波長和帶寬很容易通過電場、磁場、溫度等外界條件調(diào)控,因此可以很容易利用膽固醇液晶制備可調(diào)光學(xué)器件,比如可調(diào)光學(xué)濾波器、光開關(guān)等。其二是膽固醇液晶器件制備工藝非常簡單,只需在液晶中參雜一些手性分子,然后灌入液晶盒中便可以獲得周期性螺旋結(jié)構(gòu)的膽固醇液晶。因?yàn)檫@些獨(dú)特的特點(diǎn),近年來膽固醇液晶引起廣泛的研究興趣,包括開發(fā)在柔性顯示、光開關(guān)、可調(diào)光學(xué)濾波器等方面的應(yīng)用。研究發(fā)現(xiàn)通過在膽固醇液晶中摻雜高發(fā)光效率的激光染料,可以在無需反饋腔的情況下獲得激光輸出。因?yàn)槟懝檀家壕е苽浜唵?這一發(fā)現(xiàn)引起了廣泛的研究興趣。人們對膽固醇液晶激光進(jìn)行了大量的研究,所有這些研究大致可以歸納為兩個方面：一方面是研究可調(diào)膽固醇液晶激光,另一方面是提高膽固醇液晶激光效率。盡管人們采取不同方法提高膽固醇液晶激光的效率,但是,到目前為止膽固醇液晶激光效率仍然不高,這嚴(yán)重制約了膽固醇液晶激光器的實(shí)際應(yīng)用。為了使膽固醇液晶激光器最終能應(yīng)用到實(shí)際中去,膽固醇液晶激光效率必須進(jìn)一步提高,這正是本文研究的目標(biāo)。為了提高膽固醇液晶激光效率,本文研究了膽固醇液晶分子排列,膽固醇液晶結(jié)構(gòu)、厚度以及膽固醇液晶反射鏡的加入對膽固醇液晶激光效率的影響及其物理機(jī)制。具體研究內(nèi)容主要包括以下幾個方面：1.研究了電擊摩擦處理對膽固醇液晶分子排列的改善。研究表明隨著液晶盒厚度的增加,其內(nèi)部缺陷增多,透射率也相應(yīng)降低,而采用電擊摩擦方法處理可以明顯改善分子排列。例如對于厚度大于25μm的膽固醇液晶樣品,沒經(jīng)過任何處理之前,膽固醇液晶分子處于無序的焦錐狀結(jié)構(gòu),透射率接近于0；經(jīng)過電擊摩擦處理后,樣品變?yōu)槠矫媛菪Y(jié)構(gòu),散射明顯降低,樣品透射率由處理之前的幾乎為0提高到80%,且該方法制得的膽固醇液晶樣品能夠長期穩(wěn)定保持其平面螺旋結(jié)構(gòu)不變。本文分析了該現(xiàn)象背后的原因及其物理機(jī)制。2.研究了膽固醇液晶結(jié)構(gòu)對膽固醇液晶激光效率的影響及其物理機(jī)制。研究表明經(jīng)過電擊摩擦處理后,膽固醇液晶激光閾值降低了,同時激光效率也得到了提高,且樣品越厚,電擊摩擦處理后激光效率提高得越多,比如5μm的染料摻雜膽固醇液晶樣品經(jīng)過摩擦處理后激光效率提高了1.6倍,而50μm染料摻雜的膽固醇液晶激光效率可以提高10.7倍。本文分析了該現(xiàn)象背后的原因及其物理機(jī)制。3.研究了用膽固醇液晶作為反射鏡對膽固醇液晶激光效率的影響及其物理機(jī)制。采用與染料摻雜的膽固醇液晶同手性且?guī)捘軌蚋采w激光波長的膽固醇液晶作為反射鏡,將其放置在染料摻雜的膽固醇液晶的一側(cè),結(jié)果表明,膽固醇液晶激光效率可以得到進(jìn)一步提高,且提高的倍數(shù)隨著染料摻雜膽固醇液晶厚度的增加而降低。本文分析了產(chǎn)生該現(xiàn)象的原因及其物理機(jī)制。值得一提的是,通過摩擦處理并加反射鏡后,我們在10μm的激光樣品中獲得了最高達(dá)10%的激光效率,這是目前為止在膽固醇液晶中獲得的最高激光效率。
[Abstract]:Since the advent of the laser in the 1960s, the laser has been widely used in the fields of communication, biology, medicine, national defense and military, and has revolutionized the lives of people. The most commonly used lasers are solid-state lasers, gas lasers, dye lasers and semiconductor lasers, all of which have the characteristics of good stability, but their fatal disadvantages are bulky, which makes them increasingly unable to meet the need for integrated optical development. The development of integrated optics is more and more need of micro-laser, so the micro-laser has been widely studied in recent years. There are several types of lasers, such as the Fabry-Perot (F-P) cavity laser, the distributed feedback laser (FDB), the micro-cavity laser and the disc laser, which have the characteristics of low threshold, small volume, narrow spectrum, high modulation rate and the like. But the manufacturing process is very complicated, and the high-precision coating technology is required, and the cost is high. The cholesteric liquid crystal (CLC), because of its periodic spiral structure and high birefringence, will form a Bragg reflector, which is equivalent to one-dimensional photonic crystal. Compared with the traditional photonic crystal, the cholesteric liquid crystal has a plurality of unique characteristics. The central wavelength and the bandwidth of the cholesteric liquid crystal reflection band are easily controlled by external conditions such as electric field, magnetic field, temperature and the like, so that the adjustable optical device can be easily prepared by using the cholesteric liquid crystal, such as an adjustable optical filter, an optical switch and the like. And the other is that the preparation process of the cholesteric liquid crystal device is very simple, only some chiral molecules are involved in the liquid crystal, and then the cholesteric liquid crystal with the periodic spiral structure can be obtained after being poured into the liquid crystal box. Because of these unique characteristics, in recent years, cholesteric liquid crystal has attracted extensive research interest, including the application of developing in flexible display, optical switch, tunable optical filter and so on. It has been found that the laser output can be obtained without the need for a feedback cavity by doping a laser dye with high luminous efficiency in a cholesteric liquid crystal. This finding, because of the simple preparation of cholesteric liquid crystals, has led to a wide range of research interest. A large number of studies have been carried out on the cholesteric liquid crystal laser, all of which can be summarized in two aspects: on the one hand, to study the cholesteric liquid crystal laser, on the other hand, to improve the efficiency of the cholesteric liquid crystal laser. Although the efficiency of the cholesteric liquid crystal laser is improved by different methods, the efficiency of the cholesteric liquid crystal laser is still not high so far, which seriously restricts the practical application of the cholesteric liquid crystal laser. In order to finally apply the cholesteric liquid crystal laser to the practical application, the efficiency of the cholesteric liquid crystal laser must be further improved, which is the aim of this paper. In order to improve the efficiency of cholesteric liquid crystal laser, this paper studies the effect of cholesteric liquid crystal molecule arrangement, cholesteric liquid crystal structure, thickness and the addition of cholesteric liquid crystal reflector on the efficiency of cholesteric liquid crystal laser and its physical mechanism. The specific research contents mainly include the following aspects:1. The improvement of the arrangement of cholesteric liquid crystal molecules by electric shock friction treatment was studied. The results show that with the increase of the thickness of the liquid crystal cell, the internal defect of the liquid crystal cell is increased, and the transmittance is correspondingly reduced, and the molecular arrangement can be obviously improved by using the electric shock friction method. for example, for cholesteric liquid crystal samples with a thickness of more than 25 & mu; m, the cholesteric liquid crystal molecules are in a disordered focal conic structure before any treatment, and the transmittance is close to zero; after the electric shock friction treatment, the sample is changed into a plane spiral structure, and the scattering is obviously reduced; The sample transmittance is increased by almost 0 to 80% before the treatment, and the cholesteric liquid crystal sample prepared by the method can stably keep the plane spiral structure unchanged for a long time. This paper analyzes the reasons behind this phenomenon and its physical mechanism. The effect of cholesteric liquid crystal structure on the efficiency of cholesteric liquid crystal laser and its physical mechanism were studied. The results show that the laser threshold of the cholesteric liquid crystal is reduced after the electric shock and the laser efficiency is improved, and the thicker the sample, the more the laser efficiency is improved after the electric shock is processed. For example, a dye-doped cholesteric liquid crystal sample of 5. m u.m is increased by 1.6 times by the rubbing treatment, and the efficiency of the 50 mum dye-doped cholesteric liquid crystal laser can be increased by 10.7 times. The reason behind this phenomenon and its physical mechanism are analyzed in this paper. The effect of cholesteric liquid crystal on the efficiency of cholesteric liquid crystal laser and its physical mechanism were studied. The cholesteric liquid crystal with the same chiral and bandwidth as the dye-doped cholesteric liquid crystal can cover the laser wavelength as a reflector, and the cholesteric liquid crystal is placed on one side of the dye-doped cholesteric liquid crystal, and the result shows that the efficiency of the cholesteric liquid crystal laser can be further improved, And the multiple of the increase is reduced with the increase of the thickness of the dye-doped cholesteric liquid crystal. The reason of this phenomenon and its physical mechanism are analyzed in this paper. It is worth mentioning that, by rubbing and adding the mirror, we have achieved the highest laser efficiency of up to 10% in a 10. m u.m laser sample, which is the highest laser efficiency so far in the cholesteric liquid crystal.
【學(xué)位授予單位】：浙江師范大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TN248

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本文編號：2491111